A programmable logic controller (PLC) is used to monitor input signals from a variety of input points (i.e., input sensors) that report events and conditions occurring within a controlled process. For example, a PLC can monitor such input conditions as motor speed, temperature, pressure, volumetric flow and the like. The PLC has a control program stored within its memory to instruct the PLC on what actions to take upon encountering particular input signals or conditions. In response to these input signals provided by the input sensors, the PLC derives and generates output signals that are transmitted to control the process via PLC output points to various output devices such as actuators and relays. For example, an output signal can be provided by the PLC to speed up or slow down a conveyer, rotate the arm of a robot, open or close a relay, raise or lower temperature, as well as many other possible control functions.
The input and output points referred to above are typically associated with input modules and output modules, respectively. Input and output modules are collectively referred to as I/O modules herein. Those skilled in the art alternatively refer to such I/O modules as I/O cards or I/O boards. I/O modules are typically adapted to be plugged into respective slots located on a backplane board or other attachment system provided by the PLC. The slots are coupled together by a main bus that couples any I/O module plugged into the slots to a central processing unit (CPU). The CPU itself can be located on a card that is adapted to be plugged into a dedicated slot on the backplane board of the PLC.
In many control systems, PLCs are arranged in a master/slave network that includes a master PLC and a plurality of remote slave units that can include other PLCs or devices. In this type of a network, the master PLC controls its own I/O connection points and also the respective I/O connection points for the remote slave unit(s). The control commands from the master PLC are derived from data obtained from the remote slave units, which is obtained from the I/O module(s) connected to each remote slave unit.
To meet the needs of machine manufacturers and users, automation architectures have been decentralized or distributed while delivering performance comparable to centralized systems. For instance, the ADVANTYS STB distributed. PO system is an open, modular input/output system that makes it possible to design islands of automation managed by a master controller via a bus or communication network. The ADVANTYS STB distributed I/O system is a product of Schneider Automation Inc., One High Street, North Andover, Mass.
These automation islands, typically installed close to the machine, help reduce the time and cable cost for sensors and actuators, while increasing system availability. The island components are electronic modules mounted on one or more DIN rails (i.e., standardized rails). These clusters of modules, known as segments, carry a bus from the beginning to the end of each island. The island bus provides power distribution, signal sensing, and power management to compatible modules.
An island can include one or more segments comprising a network interface module (NIM), a power distribution module (PDM), and additional modules for various architectures such as I/O modules, bus extension modules, island bus termination, and island bus extensions.
The island is typically configured using a user interface. The NIM is responsible for assigning addresses to the I/O modules and for maintaining a process image of the I/O modules. Both the NIM and the I/O modules participate in I/O modules automatically obtaining their addresses based on their relative physical locations—using an auto-addressing protocol. The NIM is responsible for maintaining a process image of the I/O modules, which is based on the addresses of the I/O modules. Such an addressing scheme could not handle the situation where a user wanted to physically remove I/O modules that correspond to unwanted options without changing the program to add/delete the options.
Each island is comprised of several I/O modules, divided into several groups. Each group of I/O modules represents one option available in a customer's machine. When all options are included in a particular machine, then all groups of I/O modules must be physically present; this forms the “base” configuration. Different machines may contain different options, hence different groups of I/O modules.
When a machine is built, a technician uses a human-machine interface (HMI) connected to the PLC that controls the automation system and other parts of the machine to select which options are physically present in the machine. To ease PLC programming, the process image of the island must remain identical, regardless of the machine options that are chosen by the customer (and subsequently the I/O modules that are physically present).
In prior versions of automation systems, the Customer must build and maintain different island configuration files for machines with different options; this can be quite burdensome in cases where there are many combinations of machine options available. It is desired that for each base configuration, only one island configuration be necessary.
The present invention provides an I/O configuration solution to overcome these and other problems.